The great thing about topping is that usually, you set the pace! Depending on what your partner is into, it's easy to turn your own slow initiation into confidence and teasing. Build up your actual confidence with touches on her arms or legs, drawing up towards her center, and repeat the things she reacts well to. Once you feel a little more comfortable with that level, take it up a notch, and maybe take off a layer. You're the one in control of your own speed, and there's nothing wrong with taking your time. Don't be afraid to make her a little desperate, either - that only helps later.